split cleanhouse() and cleandivs()

- the idea is to *always* call cleanhouse() but only call
  cleandivs() when absolutely needed (like when we're navigating
  to a different page entirely). we'll just do .hide() or .empty()
  in the function when we need to clear something prior to append,
  or managing the visibility matrix of the regions.
  Note the existence of a "region-wide" div, which is above the
  other numbered regions, to be used for full-page things like
  holds, node/records, etc.

Signed-off-by: William Rockwood <wrockwood@tadl.org>